Apparatus and methods for geosteering

Abstract

Various embodiments include apparatus and methods to generate geosignal responses. Geosignal responses may be generated that include a representation of a determination of variation between a XX coupling component and a YY coupling component from acquired signals. Such geosignals may be used to 5 address a blindspot problem suffered in conventional geosteering in a drilling condition where the logging tool is located at layered formations with symmetric resistivity profiles. Additional apparatus, systems, and methods are disclosed.

What is claimed is: 
     
       1. A method comprising:
 acquiring compensated signals from a tool disposed in a borehole, wherein the tool comprises one or more receiving sensors and one or more transmitting sensors configured in a mutually symmetric manner with respect to a longitudinal axis of the tool along which the receiving sensors and the transmitting sensors are disposed; 
 obtaining a variation between XX and YY coupling components from the acquired compensated signals, wherein obtaining the variation between the XX and YY coupling components from the acquired compensated signals includes decoupling the XX and the YY coupling components from the acquired signals and using the decoupled XX and YY coupling components to determine the variation; 
 generating a geosignal based, at least in part, on the variation between the XX and YY coupling components; and 
 directing a drilling-related operation using the geosignal. 
 
     
     
       2. The method of  claim 1 , wherein the one or more transmitting sensors and the one or more receiving sensors are tilted with respect to the longitudinal axis of the tool such that the acquired compensated signals provide decoupled coupling components. 
     
     
       3. The method of  claim 1 , wherein the variation between the XX and YY coupling components comprises at least one of a difference between the XX and YY coupling components, a ratio between the XX and YY coupling components, or a square root of the XX and YY coupling components. 
     
     
       4. The method of  claim 1 , wherein generating the geosignal includes basing the geosignal on a combination of coupling components related to (XX−YY)/(XX+YY+2ZZ), (XX−YY)/(XX+YY−2ZZ), XX/ZZ and YY/ZZ, (XX−YY)/ZZ and (XX+YY)/ZZ, XX/(XX+YY+2ZZ) and YY/(XX+YY+2ZZ), or XX/(XX+YY−2ZZ) and YY/(XX+YY−2ZZ). 
     
     
       5. The method of  claim 1 , wherein acquiring signals includes acquiring compensated signals, and wherein the geosignal is generated from the compensated signals. 
     
     
       6. The method of  claim 1 , wherein the acquired compensated signals include signals received at the one or more receiving sensors in response to generating a transmission signal from each of the one or more transmitting sensors. 
     
     
       7. The method of  claim 1 , wherein acquiring compensated signals includes acquiring voltage signals generated based on selectively activating selected transmitting sensors of the one or more transmitting sensors and selectively collecting the signals from selected receiving sensors of the one or more receiving sensors. 
     
     
       8. The method of  claim 1 , wherein the one or more transmitting sensors and the one or more receiving sensors are antennas tilted with tilt angle having a magnitude of 45° or within one or two degrees of 45° with respect to the longitudinal axis of the tool. 
     
     
       9. The method of  claim 1 , further comprising:
 calculating coupling components for a coupling matrix using the acquired compensated signals; and 
 performing one or more inversion operations to generate formation parameters from the coupling matrix. 
 
     
     
       10. The method of  claim 1 , wherein acquiring compensated signals includes acquiring voltage signals with respect to tool orientation, the tool orientation including a number of directions, the number of directions corresponding to one complete rotation partitioned into N bins, each bin associated with an angle of rotation equal to 2π/N, N being an integer equal to or greater than one. 
     
     
       11. The method of  claim 1 , wherein acquiring compensated signals includes acquiring voltage signals generated from operating the tool rotating in the borehole. 
     
     
       12. The method of  claim 1 , wherein the method includes geosteering a drilling operation based on the geosignal. 
     
     
       13. The method of  claim 1 , wherein generating the geosignal includes generating a geosignal phase and a geosignal attenuation. 
     
     
       14. A system comprising:
 a tool having one or more transmitting sensors and one or more receiving sensors configured in a mutually symmetric manner with respect to a longitudinal axis of the tool along which the receiving sensors and the transmitting sensors are disposed; and 
 a processing unit; and 
 a machine-readable storage device having instructions executable by the processing unit to cause the system to:
 acquire compensated signals from the tool disposed in a borehole; 
 obtain a variation between XX and YY coupling components from the acquired compensated signals, wherein obtaining the variation between the XX and YY coupling components from the acquired compensated signals includes decoupling the XX and the YY coupling components from the acquired signals and using the decoupled XX and YY coupling components to determine the variation; 
 generate a geosignal based, at least in part, on the variation between the XX and YY coupling components; and 
 direct a drilling-related operation using the geosignal. 
 
 
     
     
       15. The system of  claim 14 , wherein the one or more transmitting sensors and the one or more receiving sensors include an arrangement of one or more transmitting sensors tilted substantially with respect to the longitudinal axis of the tool and one or more receiving sensors tilted substantially with respect to the longitudinal axis such that the acquired compensated signals provide decoupled coupling components. 
     
     
       16. The system of  claim 14 , wherein the variation between the XX and YY coupling components comprises at least one of a difference between XX and YY coupling component, a ratio between XX and YY coupling component, or a square root of XX and YY coupling components. 
     
     
       17. The system of  claim 14 , wherein the instructions to generate the geosignal include basing the geosignal on a combination of coupling components related to (XX−YY)/(XX+YY+2ZZ), (XX−YY)/(XX+YY−2ZZ), XX/ZZ and YY/ZZ, (XX−YY)/ZZ and (XX+YY)/ZZ, XX/(XX+YY+2ZZ) and YY/(XX+YY+2ZZ), or XX/(XX+YY−2ZZ) and YY/(XX+YY−2ZZ). 
     
     
       18. The system of  claim 14 , wherein the one or more transmitting sensors and the one or more receiving sensors include an arrangement of one or more transmitting sensors tilted substantially with respect to the longitudinal axis of the tool and one or more receiving sensors tilted substantially with respect to the longitudinal axis such that acquired compensated signals including signals received at the one or more tilted receiving sensors in response to generating a transmission signal from each of the one or more tilted transmitting sensors. 
     
     
       19. The system of  claim 14  further comprising instructions to:
 calculate coupling components for a coupling matrix using the acquired compensated signals; and 
 perform one or more inversion operations to generate formation parameters from the coupling matrix. 
 
     
     
       20. The system of  claim 14 , wherein the instructions to generate a geosignal include instructions to generate a geosignal phase and a geosignal attenuation.